PROJECT SUMMARY/ABSTRACT Disinfection of drinking water is one of the major public health achievements of the last century, but the chemical byproducts that form represent one of the most widespread exposures to potentially harmful chemicals. Optimizing the balance between the acute risk posed by pathogens and the chronic risk posed by chemical DBPs is becoming more challenging as utilities experiment with new disinfectant combinations and exploit impaired waters. We request funding for the 2017 Gordon Research Conference (GRC) on Drinking Water Disinfection By-Products (DBPs), entitled ?Disinfection 2100: Linking Engineering, Chemistry, Toxicology and Epidemiology to Reduce Exposure to Toxicity Drivers While Curtailing Pathogens.? The Conference will be preceded by a 1.5-day Gordon Research Seminar (GRS), organized by early career scientists. The GRS will feature presentations by graduate students and postdoctoral fellows, and a career mentoring panel. The GRC/GRS will present cutting-edge research to address this challenge from the fields of engineering, chemistry, toxicology, epidemiology and regulatory policy. The specific aims of this Conference differ from previous Conferences. The first aim is to broaden the scope beyond DBP formation within conventional drinking water plants to incorporate consideration of pathogens and other DBP exposure scenarios (e.g., DBPs associated with food processing). While previous Conferences discussed DBP exposures, there has been little discussion of solutions. The second aim is to move towards a solution to the DBP problem. A major strength of this conference is that it brings together engineers, chemists, toxicologists, epidemiologists and regulators, the key players for addressing this problem. The topics addressed by this GRC/GRS concur with the mission of the National Institute of Environmental Health Sciences, which is ?to discover how the environment affects people in order to promote healthier lives.? With utilities currently modifying their disinfection schemes and exploiting impaired water supplies, it is important for experts in engineering, chemistry, toxicology, epidemiology and regulatory policy to discuss the risk balance between pathogens and DBPs resulting from these new practices. The GRC/GRS format, with lengthy discussion periods and ample provision for informal discussions and social interactions, is particularly suited to promoting the needed multidisciplinary approach.